In this article: https://worldofwarships.com/en/news/development/royal-navy/ it says ->
"Premium Tier VI battleship Warspite with a slot and commander — 220 Sovereigns, can be purchased only once.
If you already have this ship in your Port and purchase it again, you'll receive 6,500 doubloons."
Thing is, if you do this now you will only get 4550 doubloons. I believe the culprit is the current anniversary event which has a discount on premium ships bought for doubloons in-game, which actually runs until the 21st so there will be overlap tomorrow as well. So even you are trading Sovereigns for a ship you are hit by this when they refund you doubloons for a ship you already have. I have sent a ticket to Support and notified @TheURLGuy so I'm hoping this is an oversight and that myself and others that did this will get the doubloons we're owed. Not sure if @Gneisenau013 could look at it if URLGuy is afk?
Also, there was no port slot addition even it said so in Arsenal.
Just a heads up people, best to wait a few days.
EDIT: Also the anniversary article states "–30% to the cost of available Premium Tier VI–VII ships in doubloons" We're using Sovereigns. They forgot to separate these two things in Arsenal/Store.
EDIT2: Sending a ticket to Support helped, they credited 1950 doubloons and apologized for the confusion.